1. Field
This disclosure pertains to a method of bonding a germanium substrate to a semiconductor substrate such as silicon substrate and a method of transferring a germanium layer to the semiconductor substrate using a low temperature and long duration annealing.
2. Discussion of Related Art
There is an increasing interest in using silicon-germanium (Sixe2x80x94Ge) alloy as a material for microelectronic and optoelectronic device applications. Germanium (Ge) is known to have high carrier mobility (e.g., high hole and electron mobility) and optical absorption as compared to silicon (Si). This is one reason why Ge is useful for devices that require enhanced performance and/or high quantum efficiency. Embodiments of devices that would benefit from the use of a Ge film include metal-oxide-semiconductor (MOS) transistors, optical detectors, and other optoelectronic devices, to name a few.
Forming high quality germanium layers on a substrate is desirable. Ge layers grown on a Si substrate can be used to make high mobility devices. Bulk Si substrates typically have lower electron and hole mobility than Ge substrates. Si typically has an electron mobility of 1500 cm2 N/s and a hole mobility of 450 cm2 N/s whereas Ge has an electron mobility of 3900 cm2 N/s and a hole mobility of 1900 cm2 N/s. Additionally, electronic devices made using bulk Si substrates require high power consumption due to current substrate leakage, especially for high performance devices. The lower mobility and the current substrate leakage problem in using bulk Si for substrate set upper limits on the performance of the electronic devices with regard to material and power dissipation aspects. On the other hand, electronic devices made with Ge require less voltage bias to turn on the devices because of the Ge""s high mobility characteristic. In addition, the use of the banded Ge to Si substrate allows the use existing infrastructure for Si substrate.
A Ge substrate can be obtained by transferring a Ge layer onto a semiconductor (e.g., Si) substrate using ion implantation, direct wafer bonding, and cleaving process. The transfer of a Ge layer onto a semiconductor substrate is difficult due to an existence of a large thermal mismatch between Ge and a semiconductor material such as Si. For embodiment, cracking, warping, and/or bowing are often observed when thermal cleaving is used to transfer the Ge onto the Si substrate.